Solar-induced chlorophyll fluorescence and its relationship with photosynthesis during waterlogging in a maize field

Solar-induced chlorophyll fluorescence (SIF) has emerged as a valuable tool for estimating gross primary production (GPP). However, the mechanism linking SIF to GPP under waterlogging stress remains unclear. Here, we investigated the GPP-SIF relationship and their responses to waterlogging stress using three years of continuous ground measurements in a maize field. Our results revealed a significant decoupling in the GPP-SIF relationship under waterlogging stress, as evidenced by a decline in R2 values from 0.87 and 0.79 (non-waterlogging years: 2020 and 2021) to 0.20 (waterlogging year:2022), consistent with SCOPE model simulations. We examined the underlying mechanisms independently regulating SIF and GPP fluctuations. Our analysis suggested a considerable transition in dominating factors influencing both parameters, shifting from photosynthetically active radiation (PAR) under non-waterlogging conditions to soil water content (SWC) under waterlogging stress. Notably, we quantified the impact of elevated SWC on GPP and SIF, finding that the effect was more pronounced on GPP (62.41% reduction) than on SIF (54.3% reduction). We observed the weakened significance of SIF mutiscattering components induced by alterations in soil background spectra due to increased SWC affecting SIF radiative transfer processes. Complemented by SCOPE simulations, our analysis suggested that the significant decoupling of SIF and GPP physiological components, along with asymmetrical responses to SWC, collectively contribute to the reduced GPP-SIF relationship under waterlogging stress. Overall, our study provides valuable insights into GPP and SIF dynamics under waterlogging stress in a maize field, emphasizing the effectiveness of radiative transfer models for understanding plant photosynthetic responses to waterlogging stress.